# An unexpected tumor-resistant phenotype from floxing PAK1 in a mouse model of colitis associated cancer

## TL;DR

Floxing PAK1 in mice unexpectedly reduced colon cancer and inflammation, suggesting a new protective mechanism.

## Contribution

The study reveals that floxing PAK1, rather than its knockout, protects against colitis-associated cancer.

## Key findings

- PAK1fl mice showed reduced inflammation and tumorigenesis compared to wild-type and PAK1KO mice.
- PAK1CKO mice had higher tumor counts than PAK1fl but were still less tumorigenic than PAK1KO or WT.
- PAK1fl and PAK1CKO mice were more resistant to microbiome shifts compared to WT or PAK1KO.

## Abstract

Inflammatory bowel disease (IBD) and colitis-associated cancer are associated with activation of PAK1 (p-21 activated kinase 1). We previously found that total knockout of PAK1 (PAK1KO) reduced tumorigenesis upon AOM/DSS but enhanced tumorigenesis in another model of IBD with total knockout of IL10 (IL10KO). To better understand the specific role of epithelial PAK1, we crossed Pak1 floxed (PAK1fl) with VillinCre mice for a conditional knockout of PAK1 in intestinal epithelia (PAK1CKO). PAK1fl were included as additional controls. Unexpectedly, inflammation and tumorigenesis were greatly reduced in PAK1fl compared to WT or PAK1KO after AOM/DSS treatment. PAK1CKO had higher tumor incidence and counts compared to PAK1fl, but was still lower in comparison to PAK1KO or WT. When crossed with IL10KO mice, PAK1CKO exacerbated the expected hyperproliferative phenotype, resulting in early mouse morbidity. Despite normal Pak1 mRNA expression in PAK1fl colonic lysates, PAK1 protein expression on immunohistochemistry was higher that WT. Both PAK1fl and PAK1CKO mice were more resistant to shifts in microbiome, and remained clustered together compared to WT or PAK1KO. Altogether, our results suggest that floxing itself may have altered Pak1 expression, which conferred protection from AOM/DSS carcinogenesis.

The online version contains supplementary material available at 10.1038/s41598-025-12082-8.